Robotic spray painting facilities are widely used in repetitive tasks and in situations where a health hazard may be involved, or where there is a special need to insure consistent results in coating quality and film thickness, for example.
Even the most skilled painters may find it difficult to apply paint with the same film thickness and quality over repeated jobs when using hand-held spray painting equipment. Moreover, where painting is repetitive, workers may find the job to be monotonous and tedious, leading to inattentiveness and reduced production and quality. Other situations may require the use of hazardous or toxic materials which are a threat to the health of workers, who may therefore be unable or unwilling to work. Many jobs also involve areas to be painted that are hard to reach, making it difficult for workers to apply a proper coating and potentially leading to reduced production and quality. For example, the lengthy air intake ducts of aircraft engines are laborious to paint with hand-held spray guns. It is difficult for workers to get into and out of these ducts, especially when fresh coats of paint have already been applied, and care must be taken to avoid nicking or scuffing of the paint that has already been applied.
Although robotic paint spraying equipment may solve these problems, some prior art spray gun apparatus require the use of a paint holding tank located remotely from the spray gun, with lengthy hoses leading from the holding tank to the spray gun. A pressure pump is also required to move the paint from the holding tank to the spray gun, and a mixing device must be used to keep the paint properly mixed during a spraying operation. Moreover, an accumulator is required in order to eliminate fluctuations in the flow of paint, and in closed loop, paint circulating systems a return line leads from the spray gun back to the pump.
Paint cure time is important, and many paints used today are two-part mixes. When the two parts are mixed together they start to cure, and the time in which a paint can be used after it is mixed is generally short. Thus, it is desirable to mix only limited quantities of paint at a time. However, because of the amount of equipment and length of hoses required in the prior art systems discussed above, several gallons of paint must be mixed in order to charge or prime the system and to provide enough paint for the job. As the paint passes through the various pieces of equipment and lengths of hoses it begins to cure and thicken. In order to maintain proper pressure at the head of the spray gun, the pump pressure must be increased. If the paint becomes too thick to flow properly, it may have to be discarded.
Further, when prior art systems are discharged, the paint that fills the various pieces of equipment and lengths of hoses is disposed of and wasted. Those items which must be emptied and cleaned include the holding tank, the accumulator, the pump, the mixing system, the hoses, and the gun itself. Cleaning fluids used to flush and clean the system are also discarded after use. If colors are changed often, or if the paint becomes too thick to use, a considerable amount of paint and cleaner are therefore wasted.
Since the paints in common use today may cost $150 or more per gallon, and two to five gallons may be wasted each time the system is discharged, the cost of materials alone required to prime and discharge a prior art system can be considerable. Moreover, the time required for priming and cleaning, and the inconvenience to the operator in use of prior art systems, contribute to increased cost.
Accordingly, there is need for a spray painting system which requires only an amount of paint to be mixed that is needed to paint an object, and which does not require an excess amount of paint just to charge the system, thereby eliminating the waste of paint and cleaning materials that occurs in prior art systems.
It would further be desirable to have a spray painting system which does not require a separate pressure pump, or system accumulator, or tank mixing system, or paint holding tank, or paint return line, thereby reducing equipment and maintenance costs. Still further, it would be desirable to provide a system that does not require complete system discharge and cleanup each time the paint is used up and/or discarded.